Mechanisms of the relaxations in (In + Nb) co-doped TiO2 ceramics

(In_0·5Nb_0.5)_0.1Ti_0·9O₂ ceramic sample was prepared by sol-gel method. The dielectric properties of this sample were investigated in a temperature range of 5–320 K. Two thermally activated relaxations were found. The low-temperature relaxation (P0-relaxation) appearing around 50 K follows the Vogel-Fulcher law and is ascribed to be a low-temperature Maxwell-Wagner relaxation caused by frozen electrons. The intermediate-temperature relaxation (P1-relaxation) occurring around 150 K obeys the Arrhenius law. Thermally activated depolarization current (TSDC) investigations reveal that it contains two relaxation processes (P1’ and P1 peaks). This relaxation was argued to be a polaronic relaxation caused by electrons hopping between Ti³⁺ and Ti⁴⁺ ions. TSDC also reveals a high-temperature relaxation (P2 peak) near room temperature, which is related to humidity sensing property.